广西北海西村港互花米草对红树林湿地大型底栖动物群落的影响

为了解互花米草(Spartina alterniflora)入侵红树林的生态影响, 作者对位于北海市西村港的红树林湿地以及周边互花米草盐沼的大型底栖动物群落多样性和群落结构进行了研究。2012年10月至2013年9月连续4次取样, 按照取样时间研究大型底栖动物的种类、物种组成、生物量和生物多样性等群落特征的差异, 探讨互花米草入侵红树林湿地对大型底栖动物的影响。本研究共采集底栖动物16种, 隶属于5门7纲15科, 其中互花米草群落10种, 红树林湿地12种。研究发现互花米草入侵后中国绿螂(Glauconome chinensis)个体数量剧增, 导致不同采样时间互花米草盐沼的大型底栖动物生物量均显著高于红树林湿地; 除个别月份外, 红树林湿地大型底栖动物的Margalef丰富度指数、Shannon-Wiener多样性指数、Simpson多样性指数和Pielou均匀度指数均显著高于互花米草群落。基于生境-采样时间的双因素方差分析结果表明, Shannon-Wiener多样性指数和Simpson指数在两种生境间差异显著; 两种生境的Margalef丰富度和Pielou均匀度指数在不同采样时间差异显著; 大型底栖动物生物量和物种数量在两种生境间和不同采样时间差异均显著。基于多元回归分析的研究结果表明, 互花米草密度是影响大型底栖动物生物量的关键因子, 而互花米草株高可以解释物种个体数量、Shannon-Wiener多样性指数和Simpson指数在两种生境的变化。对不同采样时间大型底栖动物群落结构的非度量多维度(non-metric multidimensional scaling, NMDS)分析结果表明, 红树林与互花米草群落的大型底栖动物群落相似性很低。总而言之, 在西村港地区, 互花米草入侵虽然增加了大型底栖动物的生物量, 但由于优势物种的凸显, 显著降低了大型底栖动物群落的多样性, 且种类组成与群落结构与红树林群落相比已有差异。由此可见, 互花米草入侵红树林对当地的大型底栖动物群落多样性造成影响。     

长江口潮沟大型底栖动物群落的初步研究

通过对长江口崇明东滩潮沟系统与大型底栖无脊椎动物进行取样调查 ,研究了潮沟不同生境的底栖动物群落及其多样性 ,分析了潮沟生境异质性与底栖动物群落的关系。研究发现 :①潮沟剖面中出现明显的动物群落分带现象 ,从潮沟底、潮沟边滩到草滩 ,底栖动物种类、生活型组成和生活类群比例反映了河口潮滩潮沟底栖动物生态系列 ;②密度和生物量的分布皆为潮沟边滩 >草滩 >潮沟底 ,但密度与生物量的面上群 /面下群值格局却有不同 ,说明了密度和生物量的优势生活型和生活类群随潮沟生境的差异而变化 ;③潮沟系统 3种生境的多样性指数D ,H′和J值均为草滩 >潮沟边滩 >潮沟底 ,是潮沟系统生境结构分化的结果。潮沟底和潮沟边滩等特殊生境的存在 ,提高了淤泥质河口潮滩的生境异质性 ,说明了潮沟系统在维持河口生态系统底栖动物物种多样性中的重要作用。     

长江口潮汐大型底栖动物群落的初步研究

通过对长江河口崇明东滩潮沟系统与大型底栖无脊椎动物进行取样调查,研究了潮沟在不同生境的底栖动物群落及其多样性,分析了潮沟生境异质性与底栖动物群落的关系。研究发现：①潮沟剖面中出现明显的动物群落分带现象,从潮沟底、潮沟边滩到草滩,底栖动物种类、生活型组成和生活类群比例反映了河口潮滩潮沟栖动物生态系列;②密度和生物量的分布皆为潮沟边滩＞草滩＞潮沟底,但密度与生物量的面上群／面下群值格局却有不同,说明了密度和生物量的优势生活型和生活类群随潮沟生境的差异而变化;③潮沟系统3种生境的多样性指数D,H′和J值均为草滩＞潮沟边滩＞潮沟底,是潮沟系统生境结构分化的结果。潮沟底和潮沟边滩等特殊生境的存在,提高了淤泥质河口潮滩的生境异质性,说明了潮沟系统在维持河口生态系统底栖动物物种多样性中的重要作用。     

河口盐沼植物对大型底栖动物群落的影响

通过对长江口崇明东滩盐沼海三棱燕草带大型底栖无脊椎动物进行取样调查,研究了不同盐沼底栖动物群落结构及其多样性特征,分析了盐沼植物群落特征与底栖动物群落的关系。研究发现。（1）沿着河口盐沼海拔梯度,从低位盐沼到高位盐沼,底栖动物群落结构及多样性具有明显的梯度变化;（2）盐沼植被与底栖动物群落有密切的关系,尤其是植株高度,地下部分生物量与底栖动物密度,Shannon-Weiner多样性指数,物种丰度的相关性最显著。（3）盐沼植被影响底栖动物群落,是由于植物的地下部分和地下部分结构导致盐沼生境结构复杂,增加了沉积物表层环境的结构异质性,使生境多样化,给底栖动物提供大量生活空间,（4）不同盐沼带海三陵蔗草群落的差异,提供了盐沼表层地貌的变化,这种变化及植物结构的复杂化,在这一些动物提供拓殖地的同时,也为底栖动物躲避捕食者提供了避护所;（5）盐沼植被可以改变口潮滩生境中的沉积环境,并通过消浪、缓流及调节有机质的输入动态和沉积作用而影响底栖动物群落的组成和结构。     

漩门湾不同类型湿地大型底栖动物群落特征比较研究

为研究漩门湾围垦后自然滩涂湿地和不同利用方式人工湿地7种生境的大型底栖动物群落结构现状和受扰动情况,2010年10月至2012年7月在两个区域中进行了为期两周年8个季度的大型底栖动物调查,结果表明:两周年共获得大型底栖动物5门8纲41科63种;第一周年为47种,其中自然滩涂湿地41种,人工湿地14种;第二周年为58种,其中自然滩涂湿地50种,人工湿地10种,人工湿地的物种数明显少于自然滩涂湿地。采集到的物种以软体动物和节肢动物为主,分别为32种和23种,各占总物种数的50.00%和37.10%。两周年的年均栖息密度和年均生物量在生境间从高到低依次为,年均栖息密度第一周年HSGTHHRLSCNYSK,第二周年GTHSHHSCNYRLSK;年均生物量第一周为HSRLHHGTNYSKSC,第二周年是HSHHRLGTNYSCSK。3种大型底栖动物的生物多样性指数(Margalef丰富度指数(S)、Shannon-Wiener多样性指数(H')、Pielou均匀度指数(J))分析表明,两周年7种生境3种多样性指数均处在不断的变化之中,人工湿地的Margalef丰富度指数(S)和Shannon-Wiener多样性指数(H')相对于自然滩涂湿地偏低,而Pielou均匀度指数(J)人工湿地大于自然滩涂湿地。聚类和排序的结果表明,围垦使大型底栖动物的群落结构发生明显的变化。ABC曲线分析结果表明,自然滩涂湿地受到的干扰程度较轻,而人工湿地受到的干扰程度较大。围垦改变了潮滩高程、水动力、盐度、沉积物特性,再加上人类活动的影响,这些因素是造成底栖动物群落结构及生物多样性变化的主要原因,围垦结束后的生态修复十分必要。     

长江口北支大型底栖动物群落周年变化特征

分析了长江口北支滩涂大型底栖动物的群落结构和多样性变化特征。共采集大型底栖动物78种,包括环节动物7种、软体动物23种、节肢动物28种、脊索动物18种、其它两种,全年优势种有8种。密度为0.08 ind/m^2（1月）-1.24 ind/m^2（7月）,生物量为0.006 g/m^2（2月）-0.58 g/m^2（5月）,Margalef丰富度指数（D）为0.82（1月）-3.88（7月）,Pielou均匀度指数（J）为0.60（9月）-0.86（1月）,Shannon-Wiener多样性指数（H＇）为1.59（2月）-2.76（10月）。底栖动物密度与环境因子进行相关性分析显示,北支潮间带的大型底栖动物群落按照盐度、沉积特征等不同可分为3组,盐度和温度是影响底栖动物群落分布的主导因子。     

围垦对南汇东滩湿地大型底栖动物的影响

为评价围垦促淤工程对南汇东滩湿地大型底栖动物生态学的影响,根据2004年10月和2009年10月对南汇东滩湿地底栖动物的定量定性调查数据,进行对比分析。结果表明:2004年共采集到大型底栖动物32种,其中在经围垦促淤后形成的堤内、堤外两个区域分别采集到底栖动物20种和21种,2009年堤内外分别为9种和19种,共26种;2004年堤内和堤外优势种分别为8种和4种,共有优势种为中华蜾蠃蜚和谭氏泥蟹,2009年堤内优势种仅有摇蚊幼虫1种,堤外有4种,优势种种类组成也发生了很大变化;2004年大型底栖动物的平均丰度和生物量分别为44.15个/m2和38.80 g/m2,2009年为86.76个/m2和1.97g/m2,2009年堤内、堤外的生物量与2004年相比明显降低,丰度变化则相对较小;运用SPSS软件的单因素方差分析、群落聚类和MDS排序对南汇东滩湿地各断面进行群落结构分析,结果表明围垦是大型底栖动物群落结构改变的一个重要因素,围垦造成堤内底栖动物群落结构发生了明显差异,堤外群落结构变化相对较小。大型底栖动物的生物多样性指数(Shannon-Weiner指数H'、Pielou均匀度指数J'、Margalef物种丰富度指数d和Simpson指数D)受到围垦促淤工程的影响均降低,尤其以围垦圈淤的堤内湿地生物多样性指数最低。围垦促淤工程对盐度、潮汐动力、底质特征的改变以及人类活动等因素是影响大型底栖动物群落结构的主要原因,工程结束后的湿地生态修复十分必要。     

高原深水湖泊抚仙湖大型底栖动物群落结构及多样性

云南抚仙湖是我国典型的高原深水湖泊,20世纪80年代以来,随着人类活动的加剧,其水体营养水平不断提高,生态系统发生了显著变化。为揭示该湖底栖动物的群落特征及其对生态系统变化的响应,2005年正7月对大型底栖动物群落进行了调查。在抚仙湖18个断面110个样点中共采集大型底栖动物19属27种,大型底栖动物出现率为97.3％,平均密度为855ind．／m^2,平均生物量为58．01g／m^2。在密度组成上软体动物（50．3％）〉摇蚊幼虫（32-3％）〉寡毛类（17．4％）,优势种为花纹前突摇蚊（Procladius choreus）、长角涵螺（Alocinma tongicornis）和方形环棱螺（Bellamya quadrata）,三者共占总密度的51．4％。寡毛类和摇蚊幼虫全湖性分布,而软体动物主要分布在沿岸区,各类群优势种均呈聚集分布。底栖动物在沿岸区生物量显著大于湖心区（P〈0．01）,但两者之间密度差异不显著（P〉0．05）;南区和北区之间的密度（P〉0．05）和生物量（P〉0．05）差异均不显著。相关分析表明,表层沉积物总有机碳、底层水体溶解氧是影响底栖动物密度分布的关键理化因子,而底层水体溶解氧是影响底栖动物生物量分布的关键理化因子。抚仙湖大型底栖动物群落的Pielou均匀度指数、Margalef丰富度指数、Simpson优势度指数、Shannon-Wiener多样性指数及改进的Shannon-Wiener多样性指数分别为0．74、2．88、0．87、2．40和20．84。沿岸区底栖动物多样性明显高于湖心区,主要是由于沿岸区分布有各种沉水植物,提高了底栖动物生境的异质性。与1980年调查结果相比,抚仙湖底栖动物多样性呈上升趋势,这与水体营养水平不断提高,沉水植物分布面积扩大有关。     

长江口新生湿地大型底栖动物群落时空变化格局

为了解长江口新生湿地大型底栖动物时空变化格局,2004年11月—2005年10月对九段沙湿地的3个沙洲以及各主要生境进行了调查。结果表明:九段沙湿地大型底栖动物密度和生物量均呈春季最高,夏、秋季下降,秋季末和冬季回升的趋势,整体生物多样性水平较低,分布不均匀。夏季上沙和中沙底栖动物密度存在显著差异,四季生物密度和生物量空间梯度为下沙>上沙>中沙。由物种组成分析可知,九段沙湿地大型底栖动物群落时空变化与优势种的消长有关。各季海三棱藨草带和藨草带底栖动物密度和生物量最高,芦苇和互花米草次之,光滩区域最低,且群落季节波动大。外来物种互花米草生境下底栖动物群落特征与土著种芦苇生境下无显著差异。     

珠江口底栖动物生态学研究

采泥样调查所获底栖动物一般为体形较小,活动能力较弱的种类,往往是一些底层鱼类和虾类等良好的天然饵料。珠江口海域渔业资源丰富,是中国南海区的主要渔场之一,因此,对该海域饵料底栖动物进行研究有重要意义。通过1999年9月和2000年4月分别对珠江口底栖生物进行的两个航次的采泥样调查,分别鉴定出底栖动物15衙睡21种,共计32种。底栖动物的优势种,秋季为光滑河篮蛤Potamocorbula laevis(Hinds)(Y=0.387),春季为光滑河篮蛤（Y＝0．464）和欧虫Owenia fusformis Delle Chiaje(Y=0.120)。平均个体数量和生物量,春季为591.7ind./m^2和26.7g/m^2,秋季为85.0ing./m^2和7.4g/m^2;而在各类群生物中,软体动物占绝大部分,其次为多毛类,其它各类群所占比例都不足5％。生物多样性,个体数量和生物量的分布均呈由北向南增加的趋势。另外,与近20a中的历史资料相比,珠江口底栖动物个体数量变化不大,除2000年春季较高为591.7ind./m^2外,其变化范围在72.4-128ing./m^2之间。春季生物量除1991年较高为27．0g/m^2外,变化不是很大,大约10g/m^2;但秋季生物量呈明显下降趋势,1980年为30.1g/m^2,1990年为27.8g/m^2,1999年秋季急剧下降至7.4g/m^2。此外,从底栖动物各大类群的百分组成变化情况来看,一般以软体动物个体数量（22．7％－83．2％）和生物量（57．9％－82．5％）都最高;多毛类的个体数量百分组成占第二倍,其范围是13．4％－52．3％;其它各类群的百分组成除个别时候所占比例较大外,一般都较小。     

杭州湾南岸大桥建设区域潮间带大型底栖动物功能群及营养等级的季节动态

2006年5月至2007年1月在杭州湾南岸跨海大桥附近潮滩共采集到32种大型底栖动物,根据其食性类型划分为5种功能群。用功能群方法对这些物种生境变化的关系进行了分析,结果表明:大型底栖动物各多样性指数在潮带间差异显著,季节间则只有Margalef种类丰度(S)和Shannon-Wiener指数(H′)存在显著性差异;各功能群密度在季节间均不存在显著性差异,而在潮带间除了浮游生物食者外,其它类群均存在显著性差异;肉食者的种类数在潮带间不存在显著性差异,而在季节间存在显著性差异,其它功能群刚好相反。滩涂大型底栖动物群落主要包括4个营养级别,各营养级的构成密度在季节间差异不显著,在潮带间则差异显著;各营养级种类数是处于第四级的肉食者季节间差异显著,潮带间变化不显著,处于第二、三营养等级的功能群则正好相反。底栖动物功能群多样性综合反映了杭州湾南岸大桥建设区域潮间带大型底栖动物群落变化情况。     

崇明东滩潮间带潮沟浮游动物的种类组成及多样性

为了揭示潮间带潮沟水域浮游动物的多样性, 作者于2008年4–12月在崇明东滩选取6条潮沟共18个站点进行4个季节的浮游动物采样调查。检获到浮游动物44种, 隶属于6个类群, 其中桡足类占绝对优势, 达总种类数的79.5%。分析了浮游动物的种类组成、优势种、群落结构及物种多样性等生态特征参数的季节变化。优势种有9种, 春季以细巧华哲水蚤(Sinocalanus tenellus)优势度最高, 夏季以火腿许水蚤(Schmackeria poplesia)优势度最高, 秋季以火腿许水蚤和中华华哲水蚤(Sinocalanus sinensis)优势度较高, 冬季则以四刺窄腹剑水蚤(Limnoithona etraspina)和中华华哲水蚤的优势度较高。多样性指数显示, Shannon-Wiener指数(H′)值以夏冬季较高, 物种丰富度指数(d)值以夏秋季较高, Pielou均匀度指数(J′)值以冬季最高。与崇明岛附近的长江口北港北支水域已有的研究结果相比, 种类组成差异较大, 仅有6个共有种。浮游动物的生态特征与潮汐关系密切, 涨潮时物种多样性略高于落潮时, 涨潮和落潮时优势种的种类及优势度也均呈现出一定差异。盐度、温度、径流及潮流等环境因素对潮沟浮游动物的时空分布产生了重要影响。     

Zonation of intertidal macrobenthos in the estuaries of Schelde and Ems

Based on data, collected in 1980–1990, the intertidal benthic macrofauna of the Schelde and Ems estuaries was compared. The spatial occurrence of the benthic macrofauna along the salinity gradient, including the freshwater tidal area was emphasized. Both estuaries appeared to have a very similar species composition, especially at genus level. The higher number of species observed in the Schelde estuary was probably due to a greater habitat diversity. In both estuaries species diversity decreased with distance upstream. The total density did not vary along the estuarine gradient, whereas biomass is highest in the polyhaline zone.In both estuaries distinct intertidal benthic communities were observed along the salinity gradient: a marine community in the polyhaline zone, a brackish community in the mesohaline zone, and a third community in the oligohaline and freshwater tidal zones of the estuary. These three communities were very similar between both estuaries. Their main characteristics were discussed together with the occurrence and distribution of the dominant species.For the Schelde estuary and to a lesser extent also for the Ems estuary, there was evidence that anthropogenic stress had a negative effect on the intertidal macrobenthic communities of the oligohaline/freshwater tidal zone. Only Oligochaeta were dominating, whereas the very euryhaline and/or true limnetic species were missing. In the mesohaline zone, the Schelde estuary was dominated by large numbers of short-living, opportunistic species, whereas in the Ems estuary relatively more stable macrobenthic communities were observed. A comparison with some other European estuaries showed in general similar trends as those observed for the Schelde and Ems estuaries.     

Environmental factors as forces structuring the fish community of the Elbe Estuary

Smelt, flounder, eel, three-spined stickleback, twaite shad, ruffe and herring were the major species among 62 forming the fish community of the Elbe estuary. Species richness, species diversity, evenness and total fish biomass decreased in the upstream direction. Total abundance was greatest during summer. Salinity was the most significant physico-chemical factor affecting species richness and total fish biomass, whereas water temperature was the best predictor of total abundance. Marine fish species decreased with decreasing salinity, while the freshwater species roach and ide were absent at salinities > 15‰. Bream, blue bream, white bream, perch and pikeperch occurred more frequently in shallow marginal regions with lower current velocities, while herring and other marine species occurred closer to the deep central regions with high current velocities. Annual and seasonal variations of the community structure mainly reflected in population dynamics of smelt, flounder, twaite shad, three-spined stickleback and eel, especially those of 0-age smelt. Populations of smelt and ruffe and their importance in the fish community increased between 1989 and 1992, while those of twaite shad and eel decreased. At oxygen concentrations <3 mg I¹, smelt and flounder were rare, but eels were at their maximum at 3.5 mg I⁻¹. Changes of species composition and fish abundance were closely related to daytime and tidal cycle.     

黄河三角洲典型潮沟系统水文连通性对大型底栖动物群落结构的影响

潮沟系统水文连通是滨海湿地的关键生态过程,也是维护和修复滨海湿地的重要途径。了解水文连通性如何影响生物在生境之间的扩散潜力,对于恢复和维持区域和局地生物多样性至关重要。分别于2021年春季（5月）和秋季（10月）对黄河三角洲湿地三条水文连通梯度明显的潮沟进行野外调查和原位观测,探讨不同水文连通梯度下大型底栖动物群落的时空变化特征及其影响因素。结果表明：调查共采集大型底栖动物50种,隶属4门8纲39科45属,包括环节动物23种、软体动物18种、节肢动物5种和纽形动物1种;大型底栖动物群落密度、生物量和多样性指数春季高于秋季,春季以体型小、适应能力较强的软甲类、多毛类和双壳类为主,秋季以活动能力较强的甲壳类、腹足类为主;大型底栖动物群落物种数、密度及生物量和多样性随水文连通性的升高有升高趋势,最高值出现在中等水文连通区域。研究表明潮沟系统水文连通性对大型底栖动物的栖息生境和群落结构及多样性均具有明显的影响,但群落结构及多样性随水文连通梯度的变动规律在季节间存在差异。研究结果有助于进一步了解滨海湿地水文连通对生物群落的影响机制,并为湿地环境保护和修复提供一定科学依据。     

The response of salt marsh vegetation to tidal reduction caused by the Oosterschelde storm-surge barrier

In 1986 a sluice gate barrier was completed in the mouth of the Oosterschelde estuary. The barrier has been partially or completely closed during 1986 and the first months of 1987. Consequently the high tides were reduced to such a level that the salt marshes were scarcely flooded. Since April 1987 the barrier has been closed on average during two out of 706 high tides a year. Although the barrier allows tidal exchange the tidal flow has been restricted as a result of the reduced width of the mouth of the estuary. This restriction of the tidal flow caused a 26 cm decrease of mean high water in the eastern part of the estuary. As a result the inundation frequencies of the salt marshes decreased.The response of salt-marsh vegetation to this tidal reduction was analyzed using annual records (1982 till 1990) of species composition in 57 permanent plots in two marshes at the southern shore of the estuary. Analysis of the response of individual species to marsh elevation in the pre and the post-barrier situation revealed that most species moved down the marsh elevation gradient. The first axis of an ordination (DCA-1) was significantly negatively related to inundation frequency. Between 1984 and 1990 all plots were displaced towards a significantly higher ordination score, indicating a trend towards a species composition from higher up the marsh. The position of most plots along DCA-1 remained stable until 1985 and started to increase in 1986 or 1987. The vegetation in plots dominated either by Halimione portulacoides or by Spartina anglica, started to change in 1985. This premature change was attributed to frost damage in January 1985. The initially high rate of change along DCA-1 decreased in 1989 and 1990. This would suggest that the vegetation re-equilibrated with the newly established tidal conditions. Further analysis revealed no significant difference in the relation between inundation frequency and sample score along DCA-1 between 1984 and 1990. This corroborates the view that species composition had re-equilibrated with the tidal conditions. Along DCA-2 the samples were displaced towards a significantly higher score as well. The change was attributed to an increase of the perennial Halimione and the annual Suaeda maritima. The annual Atriplex hastata displayed an increase from 1986 till 1988, but strongly declined in 1990. The transient response of this annual was described by DCA-3.During the pre-barrier phase several attempts had been made to predict the vegetation response to tidal reduction. We developed a multivariate model (CCA) with inundation frequency as a constraining factor to describe the relation between inundation frequency and species composition in the pre-barrier phase in 1984. Next we used this model to predict the score of the samples along CCA-1 in the post-barrier phase from the inundation frequencies in 1990. The actual ordination score in 1990 was calculated from the observed species composition. The predicted ordination scores did not differ significantly from the observed ones. In retrospect it is concluded that the response of the vegetation to the reduction of the tides, as far as the fraction of species composition which is related to inundation frequency is concerned, could have been predicted by our model.

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A Pleistocene disturbance event describes modern diversity patterns in tidal marsh birds

There is growing evidence to support that paleo‐timescale events are important determinants in the present‐day distribution of organisms. We explored the relationship between community composition of tidal marsh birds in the northeastern United States and potential drivers of biodiversity patterns across timescales to explore the relevance of historical contingency in this ecosystem. These potential predictors represent some of the major known influences on biodiversity in tidal marshes, including 1) a recent, intense hurricane event driving a large‐scale perturbation of this ecosystem (4 yr), 2) gradual modification of marshes through installation of human infrastructure (～ 150 yr), and 3) marsh formation and development after the Last Glacial Maximum (LGM, ～ 20 000 yr). We surveyed > 1300 locations in tidal marshes from 2011–2014 using passive point count methods to measure bird community composition at these points. We found that rarefied richness, total individuals (N), and total biomass were best explained by a quadratic relationship with marsh age peaking at 40° latitude, the location of the Last Glacial Maximum of the Laurentide ice sheet. We hypothesize that formation of marsh millennia earlier in the southern part of our survey area allowed for earlier evolution of specialization to tidal marsh by bird species than those occupying much younger, northern marshes, which could have then driven differential rates of colonization in the north (by habitat generalists) and competitive exclusion in the south (by habitat specialists). We tested this theory using a novel functional diversity metric (community habitat specialization index, or CHSI) and find that community specialization decreased linearly with marsh age, supporting our hypothesis. Our findings highlight the importance for consideration of historical contingency in biodiversity research and further exploration of mechanisms operating across geological timescales.     

Lipid biomarkers, pigments and cyanobacterial diversity of microbial mats across intertidal flats of the arid coast of the Arabian Gulf (Abu Dhabi, UAE)

Variations in morphology, fatty acids, pigments and cyanobacterial community composition were studied in microbial mats across intertidal flats of the arid Arabian Gulf coast. These mats experience combined extreme conditions of salinity, temperature, UV radiation and desiccation depending on their tidal position. Different mat forms were observed depending on the topology of the coast and location. The mats contained 63 fatty acids in different proportions. The increased amounts of unsaturated fatty acids (12–39%) and the trans/cis ratio (0.6–1.6%) of the cyanobacterial fatty acid n- 18:1ω9 in the higher tidal mats suggested an adaptation of the mat microorganisms to environmental stress. Chlorophyll a concentrations suggested lower cyanobacterial abundance in the higher than in the lower intertidal mats. Scytonemin concentrations were dependent on the increase in solar irradiation, salinity and desiccation. The mats showed richness in cyanobacterial species, with Microcoleus chthonoplastes and Lyngbya aestuarii morphotypes as the dominant cyanobacteria. Denaturing gradient gel electrophoresis patterns suggested shifts in the cyanobacterial community dependent on drainage efficiency and salinity from lower to higher tidal zones. We conclude that the topology of the coast and the variable extreme environmental conditions across the tidal flat determine the distribution of microbial mats as well as the presence or absence of different microorganisms.     

Vegetation and seed bank dynamics in a tidal freshwater marsh

Questions: What are the feedbacks among the seed bank, parent vegetation, and landscape structure that control plant species turnover in space and time in a tidal freshwater marsh? How can these feedbacks be used to better understand marsh community dynamics and to establish restoration practices that seek to restore vegetation diversity of this important and widely distributed ecosystem? Location: Potomac River, Virginia, United States (15 km south of Washington, DC). Methods: We sampled the seed bank and standing vegetation in a tidal freshwater marsh and explored similarities between seed bank and vegetation composition through space and time. We then investigated marsh surface elevation, distance to nearest tidal channels, and life history of component species as potential explanations for the observed vegetation patterns. Results: The composition of individual plots changed considerably from year to year; however, the composition at broader spatial (whole marsh) and temporal (4 years) scales was relatively stable. Species composition of the seed bank was dissimilar to both the previous and current year's standing vegetation, and similarity to standing vegetation was particularly low in plots dominated by annual species. Landscape structure and life history characteristics of individual species best explained the spatiotemporal variability in marsh vegetation. Conclusions: Restoration designs should be landscape‐dependent and explicitly incorporate spatially structured elements such as elevation gradients to maximize community diversity in reconstructed tidal freshwater marshes. Optimal designs include areas of high seed input, areas of high species turnover, as well as other areas of greater stability.